The inventive concepts disclosed within relate generally to the testing of signal paths. More specifically, the invention relates to determining a characteristic of an electronic signal path.
The benefits of being able to test signal paths are many. Some reasons are obvious. The modern world uses electronic devices that must operate reliably. Cables (or synonymously, wires) are used as signal paths in many pieces of equipment that can have catastrophic results if the equipment fails. A good example of this is an airliner. However, the consequences of non-performance do not have to be so dire in order to see that benefits are still to be gained. infrastructure of buildings and homes, where they are difficult to reach.
Testing of wires in electronic systems can be difficult, however, as the wires are often inaccessible, hidden behind panels, wrapped in protective jackets, or otherwise difficult to access. Removal of wires for testing or inspection can cause harm, and even if the wires are functioning properly upon testing or inspection, reinsertion of the wires into the system can result in damage.
Furthermore, among the most difficult wiring problems to resolve are those involving intermittent faults. For example, vibration can cause a wire with a breach in the insulation to occasionally contact other wires or surrounding items, a so-called “dry arc fault.” “Wet arc faults” occur when moisture seeps into cracked insulation, creating a conducting path for current. Because of their intermittent nature, such faults are difficult to detect. Intermittent faults can result in circuit breaker trips, particular for new smart circuit breaker technology, yet finding the source of the failure can be very difficult. Visual inspection, when possible, can fail when arc faults are too small to be detected visually.
A new type of circuit breaker, know as an arc fault circuit breaker, may actually exacerbate the challenges of detecting intermittent faults. Arc fault circuit breakers are designed to open the circuit if an arc fault is detected. Unlike conventional circuit breakers, an arc fault circuit breaker will trip even if the arc fault draws less current than the circuit breaker's maximum current rating. The goal in installing these circuit breakers is to open the circuit before damage is done to surrounding wires. But, because the circuit breaker will open before damage becomes significant, the damage can be hidden making it more difficult to detect. Also troublesome is that arc fault circuit breakers are a new technology, and may not work reliable, forcing wasted test time chasing problems that don't actually exist.
The intermittent nature of faults can be further exacerbated by differences between the typically benign environment of a service shop and the harsh realities of the operational environment. For example, in the case of an aircraft, the arc fault may only occur in the atmospheric conditions present when an aircraft is at altitude.
Finding these intermittent faults can be time consuming or even impossible using present techniques. The duration of an arc fault can be as short at 5 to 20 ms, making it virtually impossible to find using conventional testing techniques. Productive time is lost when systems must be taken out of service, yet the failures cannot be duplicated.